[#SSL_CTX_set_alpn_select_cb]
= SSL&lowbar;CTX&lowbar;set&lowbar;alpn&lowbar;select&lowbar;cb
:mrdocs:

Register the server callback that selects an ALPN protocol during the handshake&period;

== Synopsis

Declared in `&lt;openssl&sol;ssl&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
SSL&lowbar;CTX&lowbar;set&lowbar;alpn&lowbar;select&lowbar;cb(
    xref:SSL_CTX.adoc[SSL&lowbar;CTX]* ctx,
    xref:SSL_CTX_alpn_select_cb_func.adoc[SSL&lowbar;CTX&lowbar;alpn&lowbar;select&lowbar;cb&lowbar;func] cb,
    void* arg);
----

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| SSL context whose ALPN select callback is set&period;
| *cb*
| Callback invoked with the client&apos;s offered protocols, or NULL to clear&period;
| *arg*
| User pointer passed through to `cb` as its final argument&period;
|===


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